<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.js"></script>
</head>
<body>
    <ul>
        <li>0</li>
        <li>1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
        <li>5</li>
        <li>6</li>
        <li>7</li>
        <button id="even">even</button>
        <button id="odd">odd</button>
    </ul>
    <script>
        var lis = $("ul li");
        $("#even").click(function(){
            for (var i =0;i<lis.length;i++){
                if(i%2==0){
                    lis[i].style.color = "red"
                }
                else{
                    lis[i].style.color = "black"
                }
            }
        })
        $("#odd").click(function(){
            for (var i =0;i<lis.length;i++){
                if(i%2!=0){
                    lis[i].style.color = "green"
                }
                else{
                    lis[i].style.color = "black"
                }
            }
        })
    </script>
</body>
</html>